Fresh air ventilation control system

ABSTRACT

This disclosure relates to a fresh air ventilation (FAV) controller. The FAV controller may include multiple input devices for setting a target fresh air ventilation flow rate (FAVFR), an operating FAVFR for an air handler, an operating FAVFR of a first ventilation appliance, an operating FAVFR of a second ventilation appliance. The FAV controller further includes electric interfaces adapted to couple to the air handler and a thermostat for controlling the air handler, a sensor for monitoring an operation of the first ventilation appliance, the second ventilation appliance, a thermometer for monitoring temperature of fresh air in a ventilation path to the air handler, and a motorized damper disposed in the fresh air ventilation path. The FAV controller may be configured to monitor operation times of the air handler, the first ventilation appliance, the second ventilation appliance, and the thermometer via the electric interfaces, and to control the air handler and the motorized damper, and/or the second ventilation appliance via the electric interfaces.

CROSS REFERENCES

This application is based on and claim priority to U.S. ProvisionalApplication No. 62/550,878, filed on Aug. 28, 2017 and entitled “FreshAir Ventilation Control System”, the entirety of which is hereinincorporated by reference.

TECHNICAL FIELD

This disclosure relates to fresh air ventilation control (FAVC) anddirects particularly to a versatile FAVC device and method for balancedand constrained ventilation.

BACKGROUND

Air-conditioned and sealed residential or commercial constructions maybe required under applicable building codes to implement proper freshair ventilation (FAV). FAV is traditionally achieved via a fresh airduct connected to a return path of a central air handler for drawingoutside air into the building when a central fan of the central airhandler is activated. Alternatively or additionally, FAV may be providedvia unsealed openings, windows/doors that are intermittently opened,and/or the fresh air duct when other exhaust appliances, such as abathroom exhaust fan, a water heater, a dryer, a fireplace, and a rangehood, are in operation. The ventilation by the central fan and theventilation by other exhaust appliances, however, are independent of oneanother.

SUMMARY

This disclosure is directed to a FAVC device and method for balanced andconstrained fresh air ventilation.

In one implementation, an FAV controller is disclosed. The FAVcontroller may include a first input device for setting a first freshair ventilation flow rate (FAVFR) as a target for a continuous fresh airventilation, a second input device for setting a second FAVFR of an airhandler when in operation, and a third input device for setting a thirdFAVFR of a first ventilation appliance when in operation. The FAVcontroller may further include a first electric interface adapted tocouple to the air handler and a thermostat for controlling the airhandler, and a second electric interface adapted to couple to a sensorfor monitoring an operation of the first ventilation appliance. The FAVcontroller may further include a system circuitry configured to, in aconsecutive first cycle and second cycle of multiple control cycles,monitor an effective FAVFR of the first ventilation appliance during thefirst cycle based on the third FAVFR and an operation time of the firstventilation appliance during the first cycle measured via the secondelectric interface; monitor, via the first electric interface, aneffective FAVFR of the air handler during the second cycle based on thesecond FAVFR and an operation time of the air handler during the secondcycle under the control of the thermostat; and generate a control signalfor obtaining supplemental fresh air ventilation during the second cyclewhen a sum of the effective FAVFR of the ventilation appliance and theeffective FAVFR of the air handler is less than the first FAVFR.

In an alternative implementation, another FAV controller is disclosed.The FAV controller may include first input device for setting a firstfresh air ventilation flow rate (FAVFR) as a target for a continuousfresh air ventilation, a second input device for setting a second FAVFRof an air handler when in operation, a third input device for setting athird FAVFR of a first ventilation appliance when in operation, and afourth input device for setting a fourth FAVFR of a second ventilationappliance when in operation. The FAV controller may further include afirst electric interface adapted to couple to the air handler and athermostat for controlling the air handler, a second electric interfaceadapted to couple to a sensor for monitoring an operation of the firstventilation appliance, a third electric interface adapted to couple tothe second ventilation appliance, a fourth electric interface adapted tocouple to a thermometer for monitoring temperature of fresh air in aventilation path coupled to a return path of the air handler, and afifth electric interface adapted to couple to a motorized damperdisposed in the fresh air ventilation path. The FAV controller mayfurther include a system circuitry configured to monitor operation timesof the air handler, the first ventilation appliance, the secondventilation appliance, and the thermometer via the first, the second,the third, and the fourth electric interfaces; and control the airhandler and the motorized damper, and/or the second ventilationappliance via the first, the third, and the fifth electric interfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an air handling and ventilation system in a buildingincluding an FAV controller.

FIG. 2 illustrates an exemplary FAV controller having various electricinterfaces and flow rate setting devices.

FIG. 3 shows an exemplary block diagram of various components of theexemplary FAV controller of FIG. 2.

FIG. 4 illustrates an exemplary electric configuration of the FAVcontroller of FIGS. 2 and 3 in the air handling and ventilation systemof FIG. 1.

FIG. 5 shows an exemplary system logic flow of a FAV control cycle.

FIG. 6 shows an exemplary implementation of the ventilation call blockof the logic flow of FIG. 5.

FIG. 7 illustrates various constraints and conditions that may beapplied by the FAV controller in a space defined by outdoor temperatureand relative humidity of return air.

FIG. 8 illustrates a logic flow for ventilation call conditioned onmonitoring a compressor signal in cooling mode.

FIG. 9 illustrates a logic flow for ventilation call conditioned onmonitoring a compressor signal or a heating signal in heating mode.

DETAILED DESCRIPTION

Fresh air ventilation (FAV) is essential for maintaining indoor airquality in residential, commercial, industrial, and other settings. Inthe U.S., for example, ASHRAE (American Society of Heating,Refrigerating and Air-Conditioning Engineers) Standard 62.1 specifiesvarious residential FAV requirements and recommendations to builders andbuilding code designers. In particular, ASHRAE Standard 62.2 specifiesan average continuous FAV flow rate recommendation of a residenceaccording to a total floor area and number of rooms or sections. FAV maybe obtained by activation of exhaust appliances such as a central airhandler, water heaters, exhaust boosters, bathroom exhaust fans, adryer, a fireplace, and a range hood. The air exhausted by theseappliances may be replaced with fresh air via a window, door, and otherunsealed openings, and additionally, via a FAV duct coupled to a centralair handler and installed with a controllable motorized damper. Further,appliances with high exhaust flow rates or air consumptions, such ascertain types of fireplaces and kitchen range hoods, may require makeupair, necessitating an installation of fresh air intake ducts by mostbuilding codes.

The various appliances above, when activated, may produce variousexhaust flow rates. The activation of these devices may or may not becontrollable by a central device. For example, a bathroom exhaust fanmay be manually turned on and off at any time for random durationsrather than being automatically controlled. On the other hand, an FAVresulting from fresh air drawn into the building by running the centralair handler may be controllable by a thermostat coupled to the centralair handler. Some exhaust fans may be installed with dedicatedcontrollers that automatically turn on and off the exhaust fans basedon, e.g., humidity (in a bathroom for example), temperature, and otherparameters.

The FAV duct coupled to the central air handler may draw outside freshair into an air return path of the central air handler when a centralfan of the central air handler, alternatively referred to as a centralair blower, is activated. In additional to the central fan for inducingFAV (as well as internal air circulation), the central air handler mayfurther include a combination of a furnace plenum and a cooling coil ora single heat pump coil for conditioning temperature of the inside air.The cooling coil or heat pump coil may be coupled to an exteriorcompressor and an expansion valve for circulating refrigerant. Coolingand heating cycles may be controlled by a thermostat having athermometer for measuring the indoor temperature. The fresh air thatflows from the FAV duct into the return path of the central air handlermay be excessively moist and may induce condensation in the central airhandler. While the cooling coil or heat pump coil may be built to handlecondensation as a norm and thus may be affected very little by humidreturn air, condensation on a fossil fuel based furnace plenum, however,may cause gradual life-shortening corrosion.

The disclosure below relates to FAVC devices that can be customconfigured to interface with the central air handler, the thermostat,the motorized damper, and other exhaust appliances for setting,monitoring, and controlling these appliances in a holistic manner toachieve a balanced FAV that satisfies an average continuous FAV flowrate target specified by the ASHRAE Standard 62.2, subject to humidityand temperature constraints. The FAVC device disclosed below may beadapted to integrate with and control a wide range of exhaustappliances, including energy recovery ventilation (ERV) or heat recoveryventilation (HRV) systems. Further, the FAVC devices disclosed below areflexibly configured to function with a central air handler having fossilfuel based furnace plenum as well as a single heat pump coil, and tocontrol the ventilation to protect the furnace plenum fromcondensation-induced corrosion. Other advantages and improvements of thedisclosed FAVC devices over traditional ad hoc ventilation systems willbecome apparent in the detailed description below.

FIG. 1 illustrates an exemplary implementation of a residential airconditioning and FAV setting 100. Although FIG. 1 and the rest of thedisclosure below use a residential setting as an example, the underlyingprinciples discussed below are applicable to business, industrial, andother settings. As shown by FIG. 1, the air conditioning and FAV setting100 is implemented in a residence 102 and may include a central airhandler 110 coupled to a thermostat 150, one or more exhaust fans 128and 132 with exhaust ducts 130 and 134, a clothes dryer 136 with exhaustduct 138, a kitchen range hood 140 with exhaust duct 142, a fireplace190 (e.g., a gas log fireplace) with chimney 192, and an FAV controller160 coupled to the afore-mentioned appliances in an exemplary mannerthat will be described below.

The central air handler 110 may include a port 111 for returning airfrom the residence to the central air handler, a port 117 for supplyingand distributing air to various locations in the residence, a centralfan 112, a furnace with plenum 114, a heat exchanger with cooling coil116 coupled to a compressor for refrigerant 118 disposed outside of theresidence 102. When the central fan 112 is in operation, the return airin port 111 flows through the furnace plenum 114 followed by the coolingcoil 116 and is distributed throughout the residence. The furnace may becoupled to and controlled by the thermostat 150 disposed in a suitablelocation in the residence 102. The thermostat 150 may includetemperature and humidity sensors for controlling the central air handler110 to providing heating and cooling. The central fan 112 may operate atdifferent speed for cooling and heating. The furnace or furnace plenum114 may be based on combustion of fossil fuels such as oil and naturalgas. The furnace thus may need to draw combustion air from the residenceto be mixed with the fossil fuel. The required combustion air may bedrawn into the furnace combustion chambers through a furnace grill. Thecombustion exhaust may be taken out of the residence via a furnaceexhaust duct 115. A draft pipe from the outside of the residence to alocation near the furnace for replenish combustion air may further beinstalled (not shown in FIG. 1).

The central air handler may be further coupled to an FAV duct 120 at thereturn path 111. The FAV duct 120 may be extended to exit to outside ofthe residence 102. A motorized damper 124 may be installed in the FAVduct 120 to facilitate the control of flow of fresh air into the returnpath 111 of the central air handler from the outside. The motorizeddamper 124 may be placed close to the exit or a vent hood of the FAVduct 120, or alternatively, may be disposed anywhere along the FAV duct120. An outdoor temperature (ODT) sensor or thermometer 126 may beinstalled in the FAV duct 120 to measure the temperature of the airflowing from outside of the residence into the return path 111 of thecentral air handler. Sensor or thermometer 126 is referred to as anoutdoor temperature sensor but does not need to be installed outdoors.The purpose of the ODT sensor 126 is to monitor the incoming fresh airtemperature before being mixed with the air returning to the central airhandler 110. As such, the ODT sensor 126 may be installed after themotorized damper 124 but before the location of the coupling between theFAV duct 120 and the return path 111 of the central air handler 110. Forexample, a ¼ inch hole may be drilled into the FAV duct 120 and the ODTsensor may be inserted into the FAV duct via the drill hole and thedrill hole may then be sealed with metal duct tape.

The exhaust fans 128 and 132, for example, may be installed inbathrooms. They may be controlled by traditional manual wall switches.Alternatively and additionally, an ERV/HRV system may replace, e.g., theexhaust fan 128, the exhaust duct 130, and the FAV duct 120. Forexample, as shown by 170 of FIG. 1, the exhaust duct 130 of the exhaustfan 128 may be configured to exchange heat with the FAV duct 120 via aheat exchanger 180. The ERV/HRV system 170 may include separate built-infans for exhaust air and fresh air (not shown in FIG. 1). The exhaustair in the exhaust duct 130 and the fresh air in the FAV duct 120 do notmix. They only exchange heat such that the incoming fresh air ispreheated during colder weather (e.g., winters) and precooled in warmerweather (e.g., summers). In the ERV/HRV configuration, the ODT sensor126 is preferably installed after the heat exchanger 180 on the sidecloser to the return path 111 of the central air handler for purposes ofmeasuring the fresh air temperature shortly before being mixed with thereturn air at the return path 111 of the central air handler 110.

Other appliances such as clothes dryer 136, kitchen range hood 140, andfireplace 190, when in operation, may take air out of the residence withhigh flow rates. Some of these appliances, such as the fireplace 190and/or the kitchen range hood 140 may require makeup air, which may besufficiently supplied by natural drafting for large residence, or mayrequire a makeup air duct in tandem operation with these appliances (notshown in FIG. 1). According to some building code, a duct heater may befurther required for heating up cold makeup air through the makeup airduct (not shown in FIG. 1).

A central component of this disclosure, the FAV controller 160, monitorsand controls at least some of the multiple appliances above to achieveventilation requirements specified in the ASHRAE Standard 62.2 whilemaintaining quality of indoor air and protecting the furnace plenum fromexcessive moisture and condensation. The FAV controller 160, forexample, may monitor and control the FAV periodically, e.g., in 30minutes cycles, so that ventilation requirement is satisfied on averageand in each ventilation cycle.

FIG. 2 shows exemplary electric interfaces and configurable settingdevices that may be implemented in the FAV controller 160 of FIG. 1. TheFAV controller 160 may include a plurality of flow rate setting devices(FRSDs) 200. The FRSDs 200 may be implemented as rotary dialsconfigurable in multiple predetermined discrete levels of predeterminedranges as shown in FIG. 2, or may be implemented as continuous rotarydials. The FRSDs 200 may alternatively be implemented as one or morepush buttons and one or more display panels for manipulating anddisplaying a set of stored data and parameters. Other suitableimplementation for setting flow rates are contemplated. In oneimplementation, the first three FRSDs 202, 204, and 206 may be used forcomputing and adjusting ventilation runtime during each ventilationcycle according to the ASHRAE Standard 62.2. The ventilation cycleperiod, t, may be predetermined at, e.g., 30 minutes. Otherpredetermined values for t are contemplated. The FRSD 202, for example,may be used to set a continuous flow rate requirement or targetaccording to the ASHRAE Standard 62.2:

F _(target)=0.03A _(floor)+7.5(N _(br)+1)  (1)

where F_(target) is the required or target continuous ventilation ratein cfm (cubic feet per minute), A_(floor) is the floor area of theresidence (ft²), and N_(br) is the number of bedrooms (not to be lessthan 1) in the residence. As such, a 4-bedroom residence having 3000 ft²requires about 130 cfm ventilation on a continuous flow basis. The FRSD202 may be set accordingly.

FRSDs 204 and 206 may be used to set operational flow rates for thecentral fan in heating and cooling modes, F_(heat) and F_(cool),respectively. The FRSDs 204 and 206 may be used to set F_(heat) andF_(cool) in a range of, for example, from 25 cfm up to 700 cfm. Theseoperational flow rates may only include the flow rate of fresh air intothe residence via the FAV duct 120 of FIG. 1 when the central fan is inoperation. For example, flow rate of fresh air in the FAV duct 120 maybe measured using a pilot tube when the central fan is in operation andthe FRSDs 204 and 206 may be set at levels according to themeasurements. The FRSDs 204 and 206, in conjunction of the running timeof the central fan, can be used to estimate the amount of ventilationdue to cooling or heating and can be further used to estimate additionalventilation flow needed in each ventilation cycle to satisfy the targetcontinuous flow rate set in FRSD 202.

The FRSDs 210, 212, 214, and 216 may be used for setting operationalflow rate of various exhaust appliances other than the central fan. Aswill be described in more detail later, operation of the various exhaustappliances may be monitored by the FAV controller 160 and the fresh airventilation as a result of such operation during a ventilation cycle maybe tracked by the FAV controller and credited towards and reduceventilation required in one or more future ventilation cycles. The FRSDs210, 212, 214, and 216 may each be configured with various flowrate-setting ranges for monitoring different types of exhaustappliances. For example, FRSD 210 may be configured as a rotary dialwith multiple settable levels between 25-225 cfm for monitoring abathroom exhaust fan. For another example, FRSD 212 may be configured asa rotary dial with multiple settable levels between 20-140 cfm formonitoring another smaller bathroom exhaust fan. The FRSD 214 may beconfigured as a rotary dial with multiple settable levels between 80-400cfm for monitoring medium high flow rate exhaust appliances such as theclothes dryer 136 of FIG. 1. The FRSD 216 may be configured as a rotarydial with multiple settable levels between 100-1600 cfm for monitoringhigh flow rate appliances such as the kitchen range hood 140 and/or gaslog fireplace 190 of FIG. 1.

As further shown in FIG. 2, the FAV controller 160 may include anelectric interface 220 configured to couple to the central air handler110 and the thermostat 150 of FIG. 1. The electric interface 220,alternatively referred to as the central air handler interface, mayinclude a C terminal 222 for common, an R terminal 229 for providing 24V supply, a W terminal 224 for monitoring a heating signal from thethermostat 150, a GT terminal 226 for monitoring a central fan controlsignal from the thermostat 150, and a GF 228 terminal for providing afan control signal to the central air handler 110. In this exemplaryimplementation, the FAV controller 160 does not need to be connected tocompressor or cooling signal (Y) of the thermostat 150 as the thermostatfan signal (GT, 226) in conjunction with a lack of heat signal (W, 224)will suffice to signify whether cooling is active for all central airhandler configurations including central air handler based on heatpumps. The thermostat fan control signal GT 226 is passed to the GFterminal 228 though a relay contact when the FAV controller is idle oris not in control of the central fan. All terminals in the central airhandler interface 220 may source from a 24V power supply of the centralair handler 110 of FIG. 1.

Continuing with FIG. 2, the FAV controller 160 further includes twoisolated outputs 234 (V terminal pairs) and 232 (E terminal pairs)(collectively referred to as ventilation control terminals 230) foractivating/deactivating the motorized fresh air damper 124 and one ormore remote relays to control one or more auxiliary exhaust fans, e.g.,exhaust fans 128 and/or 132 of FIG. 1. The V terminal pairs may bealternatively referred to as a damper control interface and the Eterminal pairs may be alternatively referred to as an appliance controlinterface. Both the V terminal pairs and E terminal pairs may becompatible with all types of ERV/HRV systems that may use dry contact orDC signals. In one implementation, both the V and E terminal pairs maybe isolated from the 24V supply, and as such, one terminal of each pairmay be connected to the R (24V) side of a supply transformer in order tocontrol the motorized damper 124 or the remote relay to operate theexhaust fan 128.

The FAV controller 160 may further include an outdoor temperature (ODT)monitoring interface with terminals S (260 of FIG. 2) for coupling tothe ODT sensor 126 of FIG. 1 for monitoring the temperature ofventilation air drawn into the FAV duct from the outside. In oneimplementation, the ODT sensor is not polarized so it does not matterwhich wire is connected to either of the S terminals. The FAV controller160 may further provide a three color (Red, Green, Blue) LED 270 as aclimate condition indicator to indicate condition of outside airtemperature and relative humidity of the return air, as will bedescribed in more detail below.

Continuing with FIG. 2, the FAV controller further provides appliancemonitoring electric interface 240 for monitoring various exhaustappliances during each ventilation cycle. The purpose of the monitoringis to account for ventilation achieved by the various exhaust appliancesand credit such ventilation to future ventilation cycles for optimizingenergy usage and for preventing over ventilation. In one implementation,the appliance monitoring electric interface 240 may include four pairsof terminals, 241/242 (A1/AC1), 243/244 (A2/AC2), 245/246 (A3/AC3), and247/248 (A4/AC4) for independently monitoring up to four exhaustappliances. Specifically, each of these terminal pairs may be connectedto a current sensor in the electric path or a pressure or flow sensor inthe air path of an exhaust appliance for monitoring an operation of theexhaust appliance. The current sensor, for example, may determinewhether the exhaust appliance is electrically energized. The pressuresensor/airflow sensor, for another example, may determine whether theexhaust appliance is energized by detecting air pressure/airflow valuesor changes. The operation time of the exhaust appliance during eachventilation cycle may be tracked. The four pairs of monitoring terminalsmay be electrically isolated from each other. Unused pairs of monitoringterminals may be left unconnected. The four FRSDs 210, 212, 214, and 216described above specifies the corresponding operational flow rates ofthe exhaust appliances monitored by the four pairs of monitoringterminals. An FRSD setting is effective only when the corresponding pairof monitoring terminals are connected to a sensor and detect operationof the corresponding exhaust appliance. In some implementation, eachmonitoring pair of terminals may be used to monitor a group rather thana single appliance via, e.g., multiple disjunctively connected currentsensors.

The FAV controller may further include a mode selector 250 for settingvarious mode of ventilation control operation. In one exemplaryimplementation, the mode selector 250 includes four dipswitches 252,254, 256, and 258 (positions 4, 3, 2, and 1). For example, as shown inTable 1 below, the dipswitches at positions 1 and 2 may be used forspecifying a climate setting; the dipswitch at position 3 may be usedfor specifying a central fan circulation control mode; and the dipswitchat position 4 may be used to specify an energy mode for the FAVcontroller 160.

TABLE 1 POS 1 POS 2 HOT COLD FUNCTION ON ON NORMAL OFF ON COLD ON OFFHOT OFF OFF DISABLED FUNCTION POS 3 ON FAN CYCLES WITH APPLIANCE #3INPUT OFF FAN DOES NOT CYCLE WITH APPLIANCE #3 INPUT POS 4 ON ENERGYSAVING MODE, EXHAUST FAN CONTROL, CENTRAL FAN NOT CONTROLLED BY FAVC OFFDISABLED, FAVC CONTROLS CENTRAL FAN

Specifically, the climate mode specified by the dipswitches at positions1 and 2 of the mode selector 250 may be used to determine constraintsand conditions on the ventilation control by the FAV controller 160during each ventilation cycle based on climate. The effect of theseconstraints and conditions will be described in more detail below. Thecentral fan circulation control mode specified by the dipswitch atposition 3 of the mode selector 250 may be used to determine whether theFAV controller needs to bypass the thermostat fan control and force thecentral fan to turn on when the FAV controller detects an operation of aparticular exhaust appliance. In one exemplary implementation, thecentral fan circulation control mode may be tied to an appliancemonitored by the appliance monitoring terminals A3/AC3 (245 and 246 ofFIG. 2). As such, if the dipswitch at position 3 is set to “ON”, the FAVcontroller will bypass the thermostat and turn on the central fan viathe GF terminal 228 of the central air handler interface 220 when itdetects that the appliance monitored by the A3/AC3 terminals is inoperation. If the dipswitch at position 3 is set to “OFF”, the operationof the appliance monitored by the A3/AC3 terminals would have no effecton the operation of the central fan. This feature is useful because somehigh flow rate appliances such as the clothes dryer 136 of FIG. 1 maylocally remove air in a particular room of the residence and it may bedesirable to force the central fan to circulate and balance air in theentire residence when such a high flow rate appliance is in operation.

The energy mode set by the dipswitches at position 4 of the modeselector 250 specifies whether the FAV controller controls ventilationin a normal mode or in an energy saving mode. In the energy saving mode,for example, additional ventilation required in each ventilation cycleafter taking into account the ventilation by the central fan under thecontrol of the thermostat during heating or cooling calls may beobtained by controlling an exhaust appliance (e.g., an exhaust appliancecoupled to an efficient ERV/HRV setup such as 170 of FIG. 1) by theappliance control terminals 232 (E terminals) of the FAV controller 160without controlling the central fan. In the normal mode, the additionalventilation required in each ventilation cycle may be obtained byactivating the central fan (if not activated already by the thermostat)via the GF terminal of the central air handler interface 220 in additionto activating the exhaust appliance controlled by the ventilationcontrol terminals 232 (E terminals). In the energy saving mode, the flowrate of the appliance controlled by the E terminals may be set by theFRSD 210. Such an appliance may further be monitored by the A1/AC1terminals corresponding to the FRSD 210. The E terminals may controlmore than one appliances by connecting the E terminals to multiplerelays, each for activating/deactivating one appliance. In someimplementations, the mode selector 250 may further include a fifthdipswitch 259 for implementing an Auto/On function. In conjunction withthis function, the FAV controller may further include remote controlterminals (RA and RB as part of, e.g., central air handler interface220) that may be used by a remote control of the FAV controller (whenthe installed location of the FAV controller is too difficult to accessdirectly). In particularly, the remote control terminals may be drycontact and the a remote control may connect to the remote controlterminal by a timer control, a toggle switch, or the like. The remotecontrol, when connected to the FAV controller via the remote controlterminals RA and RB, would control the on/off of the FAV controller. IFthe remote control terminals RA and RB is not connected to any remotecontrol, the dipswitch 259 may function as a on/off switch for the FAVcontroller. In some implementations, the FAV controller may stillrespond to make up air function by monitoring, for example, terminals247 and 248 for operation of appliances needing makeup air and activateventilation regardless of whether the FAV controller is set at off stateeither by the remote control via the RA and RB terminals or by thedipswitch 259 directly.

FIG. 3 further illustrates an exemplary block diagram of the FAVcontroller 160. In particular, the FRSDs 200, the central air handlerinterface 220, the damper control interface 234, the appliance controlinterface 232, the appliance monitoring interface 240, the mode selector250, the ODT monitoring interface 260, and the climate conditionindictor 270 are coupled and provisioned by the system circuitry 300.The system circuitry 300 may further be electrically coupled to arelative humidity (RH) sensor and indoor thermometer 310 mounted on theFAV controller, a data storage/registers 320 for storing settingparameters and other parameters such as credit timer values discussedbelow, and an instruction memory 330 for storing instructions orfirmware of the FAV controller. The memory may be of any suitable type.For example, the memory may be a non-transitory read-only memory. Thesystem circuitry 300 may include a processor and other digital oranalogue circuitry. The processor, for example, may be amicrocontroller, a central processing unit, a field programmable gatearray, or any other type of processor capable of executing instructionsand performing the functions of the FAV controller 160.

FIG. 4 shows an exemplary connectivity between the FAV controller andvarious appliances, devices, and sensors with reference to theresidential setting of FIG. 1. Specifically, the terminals of thecentral air handler interface 220 are connected to correspondingterminals of the thermostat 150 and the central air handler 110. Thecentral fan control terminal 401 of the thermostat 150 is connected tothe GT terminal 226 of the FAV controller 160 rather than directly tothe fan control terminal 403 of the central air handler. This allows theFAV controller either to relay the fan control signal from thethermostat to the central air handler or take control of the central fanof the central air handler for ventilation or circulation if needed. Theheat signal terminals W of the thermostat 150, the FAV controller 160,and the central air handler 110 are connected. As such, heating isdirectly controlled by the thermostat and the FAV controller may monitorheat calls. The cooling control terminal Y of the thermostat 150 isconnected to the central air handler for control cooling but need not beconnected to the FAV controller. The FAV controller may monitor coolingcalls by analyzing the fan control signal GT and the heating controlsignal. Further, the damper control terminals 234 of the FAV controlleris connected to the motorized damper 124. The ODT monitoring interface260 is connected to the ODT sensor 126.

FIG. 4 illustrates four exhaust appliances that are monitored and/orcontrolled by the FAV controller 160, including the exhaust fans 128,132, the clothes dryer 136 and the kitchen range hood 140 of FIG. 1. Theoperation of these exhaust appliances may be monitored by the sensors402, 404, 406, and 408 disposed in the electric supply or return pathsof these appliances. The operations of these devices may be at randomtimes and for random durations. For example, an occupant of theresidence may turn on the wall switches 420 and 422 of the exhaust fans128 and 132 at any time and for any length of time. Sensors 402, 404,406, and 408 are correspondingly connected to the appliance monitoringinterface 240 of the FAV controller. Sensors 402, 404, 406, and 408 maybe of any suitable type, e.g., current sensors disposed in theelectrical paths of the exhaust appliances, such as Hall Effect sensors,current clamp meters, fluxgate transformer type of sensors, fiberoptical current sensors, Rogowski coil sensors, and the like, and/orpressure/airflow sensors disposed in the air paths of the exhaustappliances. The exhaust fans 128 and 132 may further be controlled bythe appliance control interface 232 (the E terminals) of the FAVcontroller via relays 412 and 410. In the example of FIG. 4, bothexhaust fans 128 and 132 are controllable by the FAV controller. Inother alternative implementations, only one of the exhaust fans may becontrolled and the E terminals of the FAV controller may accordingly beonly connected to control one of the two relays 410 and 412.

The FAV controller of FIGS. 1-4 may be configured to execute a firmwarestored in the instruction memory 330 of FIG. 3 to perform variousventilation monitoring and controlling functions. Ventilation controlmay be performed in ventilation cycles. In each cycle, the FAVcontroller monitors and controls various appliances and devices tosatisfy the ventilation target while maintaining air quality, monitoringthe humidity and temperature constraints for protecting the furnaceplenum from condensation. An exemplary logic flow in one ventilationcycle is illustrated in FIG. 5. The ventilation cycles may run on apredefined periodicity t. The cycle periodicity t, for example may be 30minutes, as shown by 501 of FIG. 5, or may be set at any other suitabletime period.

As illustrated by the exemplary implementation 500 of FIG. 5, the FAVcontroller 160 may perform one or more of several parallel processes502, 504, 506, 508, and 509 during each ventilation cycle 501. Inprocess 508, the FAV controller monitors operation of the exhaustappliances coupled to the appliance monitoring interface 240 of FIGS.2-4 via sensors 402, 404, 406, and 408 of FIG. 4 (520). The variousexhaust appliances may be monitored independently and their operationtimes within the ventilation cycle may be separately tracked. Theseexhaust appliances may be activated manually by an occupant of theresidence at any random times and for any durations. In oneimplementation, the effective fresh air ventilation as a result of theoperation of these exhaust appliances may not be taken into accountduring the current ventilation cycle but may be credited towards thenext one or more cycles. The operation time of each appliance in thecurrent ventilation cycle may be normalized towards the continuousventilation flow requirement or target of the ASHRAE Standard 62.2 asspecified by the FRSD 202 of FIG. 2.

Specifically, if the monitored operation time for an exhaust appliancecoupled to terminals A1/AC1 (terminals 241 and 242 of FIGS. 2 and 3) ist_(A1-actual), and the operational flow rate of this exhaust applianceas specified by FRSD 210 of FIG. 2 is F_(A1), then the normalizedoperation time for the this exhaust appliance during the current cyclemay be determined as:

t _(A1-Normalized) =t _(A1-actual) *F _(A1) /F _(target)  (2)

where F_(target) is the target continuous flow rate as specified by theASHRAE Standard 62.2 via Equation (1) and set in the FAV controller 160by the FRSD 202 of FIG. 2. As such, the operation time of the exhaustappliance in the current ventilation cycle is normalized to anequivalent time of ventilation at the continuous target ventilation flowrate. Independent monitoring and normalization of operation times ofother appliances via A2/AC2, A3/AC3, and A4/AC4 terminals (terminals243-247 of FIGS. 2 and 4) are similar. As such, normalized operationtimes t_(A1-Normalized), t_(A2-Normalized), t_(A3-Normalized), andt_(A4-Normalized) may be independently tracked and used to credittowards ventilation target for the next one or more ventilation cycles(the credit may be sufficient to credit more than one cycle because thenormalized operation times may be more than t of, e.g., 30 minutes).Each of these normalized operation times may be used to set a credittimer for the next one or more ventilation cycles. As such, fourindependent credit timers may be established according to this specificimplementation.

In one implementation, the normalized operational timest_(A1-Normalized), t_(A2-Normalized), t_(A3-Normalized), andt_(A4-Normalized) (or the credit timer values) may be capped. Forexample, appliances with relatively small ventilation flow rates, suchas those exhaust fans monitored by the A1/AC1 and A2/AC2 terminals ofthe FAV controller, may be limited to 30 minutes, or one ventilationcycle worth of credit. Appliances with medium ventilation flow ratessuch as a clothes dryer monitored by the A3/AC3 terminals of the FAVcontroller may be capped at 60 minutes, or two ventilation cycles worthof credit. Appliances with high flow rates such as those monitored bythe A4/AC4 terminals of the FAV controller, on the other hand, may belimited to 240 minutes, or eight cycles worth of credit.

In some other implementation, the normalized operation timest_(A1-Normalized), t_(A2-Normalized), t_(A3-Normalized), andt_(A4-Normalized) (or the credit timer values) may further be weighteddownwards considering that some appliances may not obtain the fullspecified ventilation flow rates, when, for example, the motorizeddamper is closed when the appliances are in operation, and draft offresh air into the residence may not be sufficient for the appliances toexhaust at the specified flow rates. The weighting factor may bepredetermined for each appliance. The operation state of the damper maybe further monitored (via the V terminals of the FAV controller of FIGS.2 and 4) and the normalized operational time of the appliances may onlybe weighed downwards for the portion of time when the damper is notopen.

In one implementation, the appliance monitoring process 508 may be usedto enable other functions and controls by the FAV controller 160. Forexample, a high flow rate appliance requiring makeup air may bemonitored by the A4/AC4 terminals of the FAV controller. The FAVcontroller may be configured to force the motorized damper to open viathe V terminals of the FAV controller and force the central fan tooperate when it detects that the high flow rate appliance is inoperation, irrespective of whether a fresh air ventilation call isneeded during the ventilation cycle, whether heating/cooling is active,or whether there are any humidity and temperature constraints. Foranother example, some high flow rate appliance, such as a clothes dryer,may cause local ventilation that is unbalanced at the level of theentire residence. This type of appliances may be monitored by the A3/AC3terminals of the AV controller. By setting a central fan circulationcontrol mode specified by the dipswitch at position 3 of the modeselector 250 of FIG. 2 to ON (see description above), the FAV controllermay be configured to bypass the thermostat and turn on the central fanwhen it detects an operation of the appliance at terminal A3/AC3,irrespective of whether heating or cooling by the thermostat orventilation call by the FAV controller is active. Activating the centralfan in such a situation helps balance the local ventilation to theentire residence.

Continuing with the logic flow of FIG. 5, the FAV controller 160 mayfurther perform the parallel processes 506 and 504 for monitoringbeginning and ending of any of heating or cooling call by the thermostatduring the current ventilation cycle (530 and 540). Such monitoringfunctions can be achieved via the W and GT terminals of the FAVcontroller (terminals 224 and 226 of FIGS. 2 and 4). In response todetecting a beginning or ending of a cooling or heating call, the FAVcontroller records the indoor temperature and relative humidity (RH) atthe return path of the central air handler using the built-inthermometer and humidity sensor 312 of FIG. 3. As such, the FAVcontroller is preferably mounted on the return path of the central airhandler with the indoor thermometer and humidity sensor 312 exposed tothe air returning to the central air handler. In one implementation,only the most recent pairs of heating/cooling call start and end indoortemperature and RH are tracked. The most recent pair of beginning andending heating/cooling call RH and temperature may be used forpredicting the next heating/cooling call.

Optionally in one implementation, when a beginning of a heating orcooling call is detected in process 504 of FIG. 5, the FAV controllermay immediately end the current ventilation cycle and start the nextventilation cycle, irrespective of whether the current cycle time t of,e.g., 30 minutes, has expired, as shown by the logic flow step of 542 ofFIG. 5.

Continuing with FIG. 5, the FAV controller may implement ventilationcontrol functions during the current ventilation cycle in process 502.Specifically, at 510, the FAV controller may first wait for all theindependent credit timers set from previous cycles to expire beforeproceeding. If any of the credit timers is more than t (501), thecurrent ventilation cycle may continue to the end without ventilationintervention in process 502 by the FAV controller.

In process 502, once all the credit timers lapse during the currentventilation cycle (after t_(c), 519), the FAV controller may performventilation call 512 for a duration t_(v) (514) such that theventilation target for the current cycle is satisfied. During theventilation call, various constraints and conditions may be monitored(516) by the FAV controller and the ventilation call may be terminatedor the ventilation duration may be reduced when the constraints andconditions prohibit a full ventilation for, e.g., the protection of thefurnace plenum from condensation. Once the ventilation target issatisfied, the ventilation call ends and the ventilation cycle continuesfor an idle period ti (518) until the current ventilation cycle ends andthe FAV controller enters the next ventilation cycle.

The process 509 of FIG. 5 may be used by the FAV controller to force thecentral fan to circulation air in the residence. Circulation of air maybe forced when the FAV controller is set to energy saving mode, and thecentral fan has been idle for a predetermined extended period of time,e.g., 4 hours, either because the thermoset is turned off orheating/cooling is not triggered. The forced circulation may beconfigured to last for, e.g., one ventilation cycle.

FIG. 6 illustrates an exemplary logic flow for the ventilation call 512in more detail. The FAV controller first determines a length of theventilation call (602, 604, and 606). To determine the length of theventilation call, the credit time t_(c) of FIG. 5 is first taken off anormalized ventilation target time t_(target), e.g., 30 minutes. Thelength of the ventilation call is determined by:

t _(v)=(t _(target) −t _(c))*F _(target) /F _(exp)  (3)

where F_(exp) is an expected ventilation flow rate during theventilation call. The expected ventilation flow rate depends on whichand how many ventilation appliances are expected to be in operation forthe ventilation call.

Thus, as shown in FIG. 6, in one implementation, the FAV controller maycalculate the length of the ventilation call differently depending onwhether the heating or cooling by the central air handler is active atthe time the ventilation call begins (610). When heating/cooling isactive (branch 601), as monitored via the W and GT terminals of the FAVcontroller in FIGS. 2 and 4, the FAV controllers calculate the runtimeof the ventilation call assuming that the central van will continue tobe on under the control of the thermostat, giving rise to a ventilationflow rate as set in FRSD 204 or 206 of FIG. 2. The calculation of theruntime of the ventilation call (602) in branch 601 thus may beirrespective of whether the FAV controller is set in the normal mode orthe energy saving mode via the position 4 of the mode selector 250 ofFIG. 2 and Table 1 (e.g., step 614 is after step 602 in FIG. 6). The FAVcontroller will activate the E terminals (232 of FIGS. 2 and 4) to turnon any controlled exhaust appliances. The flow rate of these appliances(set in the FRSD 210 of FIG. 2) may either be added to the ventilationflow rate of the central fan when calculating the runtime of ventilationcall in the current cycle, or be disregarded but credited as monitoredin process 502 of FIG. 5 to the next one or more ventilation cycles.Thus, the runtime of the ventilation call calculated in 602 may be basedon Equation (3) using, as an effective flow rate Fex_(p), the flow rateof the central fan in either heating or cooling mode and optionallycompounding the flow rate of the exhaust appliance to be activated bythe E terminal of the FAV controller.

However, if the FAV controller detects that heating/cooling is notactive (branch 603 of FIG. 6), the runtime of the ventilation call maythen depend on whether the FAV controller is set in the normal mode orthe energy saving mode, as shown by 612, 604, and 606 of FIG. 6. In thenormal mode, because the FAV controller will turn on the central fan viathe GF terminals of FIGS. 2 and 4 as well as any exhaust applianceconnected to the E terminals of the FAV controller, the expected flowrate F_(exp) of Equation (3) for calculating the runtime of theventilation call may be the ventilation flow rate of the central fan andoptionally the sum of the ventilation flow rate of the central fan andthe controlled exhaust appliances (604, similar to 602). In the energysaving mode, because only the controlled exhaust appliance will be inoperation in the absence of heating or cooling, the expected flow rateF_(exp) of Equation (3) for calculating the runtime of the ventilationcall may only include the flow rate of the controlled exhaust applianceas set by the FRSD 210 of FIG. 2 (606).

Continuing with FIG. 6, once the runtime of the ventilation call isdetermined in 602, 604, and 606, the FAV controller activates its Vterminals to open the motorized damper of FIGS. 1 and 4 and furtheractivates the exhaust appliances controlled by terminal E of FIGS. 2 and4 (see steps 620, 622, 624, and 626 of FIG. 6). In 620, under energysaving mode and when heating or cooling is active, the central fan maystill be in operation as controlled by the thermostat even if the FAV isoperating in the energy saving mode. In 622 (normal mode withheating/cooling active), the FAV controller needs not to control thecentral fan because the central fan is already on as controlled by thethermostat. In 624 (normal mode with heating/cooling inactive), the FAVcontroller further turns on the central fan via the GF terminal of FIGS.2 and 4. In 626 (energy saving mode with heating/cooking inactive), thecentral fan is not turned on by the FAV controller and remains inactive.

Continuing with FIG. 6, following step 620, and in step 630, if the FAVcontroller detects an end of the heating or cooling call in the energysaving mode before the runtime of ventilation call has lapsed, the FAVcontroller will not keep the central fan on and may adjust the runtimeof the ventilation call considering that the central fan is now off andthe ventilation flow rate has dropped. Upon the adjustment of theruntime of the ventilation cycle, the FAV controller keeps the motorizeddamper open and keeps the E terminal active until the end of theadjusted runtime of the ventilation call or the end of the currentventilation cycle.

Following step 622 of FIG. 6, and in 632, if the FAV controller detectsan end of the heating or cooling call in the normal mode before theruntime of ventilation call has lapsed, it may further determine whetherthe ended heating or cooling call was a long call or short call, where along call may be a call that is longer than a predetermined thresholdof, e.g., 5 minutes, and a short call may be a call that is equal to orshorter than the predetermined threshold. In one implementation, if theheating or cooling call was a long call, the FAV controller mayterminate the ventilation call and go into idle (636). If the heating orcooling call was a short call, then the FAV controller may continue withthe ventilation if the remaining ventilation time is equal to or lessthan a predetermined amount (e.g., 5 minutes) and may terminate theventilation and go into idle if the remaining ventilation time is longerthan the predetermined amount (short call procedure in normal mode 638).

Following step 626 of FIG. 6, and in 634, if the FAV controller detectsa beginning of a heating/cooling call in the energy saving mode beforethe runtime of ventilation call has lapsed, the FAV controller mayadjust the runtime of the ventilation call considering that the centralfan is now turned on by the thermostat and the ventilation flow rate hasincreased. Upon the adjustment of the runtime of the ventilation cycle,the FAV controller keeps the motorized damper open and keeps the Eterminal active until the end of the adjusted runtime of the ventilationcall or the end of the current ventilation cycle.

The ventilation call 512 of FIG. 5 may be aborted or reduced in runtimeat any time when one or more of a predefined set of constraints aredetected in 516. These constrains may be designed for maintaining theair quality (e.g., humidity level) and for protecting the furnace plenumfrom condensation. These constraints, for example, may be based on theODT and RH of return air into the central air handler. FIG. 7illustrates examples of these constrains represented in a space of ODT(vertical axis) and RH (horizontal axis).

As shown in FIG. 7, a high temperature threshold 704 and a lowtemperature threshold 702, e.g., T_(high)=100° F. and T_(low)=17° F.,may be set for the ODT. Accordingly, the FAV controller may beprogrammed to terminate any ventilation call by, e.g., closing themotorized damper and turning off controlled ventilation appliances whenthe ODT sensor 126 of FIGS. 1 and 4 detects these temperature extremesin the ventilation air in the FAV duct 120 of FIG. 1 before entering thereturn path 111 of the central air handler.

For another example in FIG. 7, the FAV controller may be configured torequire heating to be active when the ODT is less than a heatingtemperature threshold T_(heat) 710, e.g., T_(heat)=40° F. As such, theFAV controller may be configured to monitor the ODT via the ODT sensorand terminate any ventilation call if the ODT is less than T_(heat) andthe heating is not active. For yet another example, the FAV controllermay be configured to reduce ventilation when it detects that the ODT isbelow a low ventilation reduction threshold T_(low-reduction) 706, e.g.,T_(low-reduction)=25° F. The ventilation requirement and thus thecorresponding ventilation call runtime may be adjusted to apredetermined percentage, e.g., 25%, of the target. The FAV controllermay be configured to similarly reduce ventilation when it detects thatthe ODT is above a high ventilation reduction thresholdT_(high-reduction) 708, e.g., T_(high-reduction)=90° F.

For another example, the FAV controller may be further configured toprohibit ventilation when it determines that the mixed ventilation airand return air at the central air handler is below a low mixed airtemperature threshold T_(low-mixed), e.g., T_(low-mixed)=55° F. The FAVcontroller may determine the mixed air temperature using the ODT sensorreading and its built in indoor thermometer 310 of FIG. 3 based on, forexample, psychrometric calculations.

Further, as shown in FIG. 7, the FAV controller may be configured suchthat when the ODT is below T_(heat) (710 of FIG. 7, e.g., 40° F.) and ifthe RH measured by the FAV controller using the humidity sensor 310 ofFIG. 3 is above a first RH threshold H₁ 720, e.g., H₁=55% and is notdropping during a ventilation cycle, the ventilation may be reduced (orcanceled if ODT is below T_(low) 702). Further, the FAV controller maybe configured to permit ventilation when the ODT is between T_(heat) 710and T_(RH) 712 (e.g., T_(RH)=85° F.) as long as the RH is belowthreshold H₁ 720. If the ODT is between T_(RH) 712 andT_(high-reduction) 708, the FAV controller may permit ventilation if theRH does not exceed a second RH threshold H₂ 730, e.g., H₂=65%.

The various thresholds temperatures and threshold RHs in FIG. 7 and thedescription above are only intended as examples. These settings may beconfigurable according to the climate mode as set by positions 3 and 4of the mode selector 250 of FIG. 2 and Table 1. FIG. 7, for example, maybe intended for a set of thresholds for the normal climate mode. Thesethresholds may be different for the cold climate and hot climate modes.For example, T_(low) may be set at 0° F. rather than 17° F. and T_(heat)may be set at 50° F. rather than 40° F. for the cold climate mode.Further, the LED climate indictor 270 of FIG. 2 may be configured atvarious predetermined color for indicating which region in the ODT-RHspace the FAV controller is operating in.

In the implementations described above with respect to FIGS. 2 and 4-7,the cooling signal (Y) from the thermostat (shown as 405 in FIG. 4) isnot connected to the FAV controller 160 and is not utilized indetermining ventilation calls. determination of cooling calls are basedon composite signal from the heating signal 224, central fan signal 226of FIG. 2, as described above with respect to FIG. 2. In some otheralternative implementations as described below, such cooling signal(used to active compressor 118 of FIG. 1) may be connected to the FAVcontroller 160 and utilized for controlling the ventilation. In theseimplementations, the FAV control terminals of FAV controller maycorrespondingly include in the central air handler interface 220 of theFAV controller 160 (see, e.g., FIG. 2) a cooling terminal 223 (alsodenoted by “Y”) along with the C (222), W (224), GT (226), and GF (228)terminals. In a system using heat pumps, the compressor signal indicateseither cooling or heating, depending on the ambient temperature. Furtherfor heat pumps, Y (223 of FIG. 2) or W (224 of FIG. 4) may be active forheating. Conventional systems may use Y for cooling and W for heatingpurposes. Monitoring the Y terminal helps to identify when thethermostat is calling for cooling or heating (heat pump) so thecontinuous fan operation can be ignored. These implementations allow fora means to differentiate a condition where the thermostat is set tocontinuous fan but may be turned off for providing temperature control,or the homeowner has a preference for air flow distribution though thehome at all times. Compared to the implementations described above inFIGS. 2 and 4-7, in these alternative implementations, the determinationof start and end of cooling calls in process 504 and 506 would be basedon the compressor or cooling signal Y (monitored by terminal 223 of FIG.2 from the thermostat terminal 405 of FIG. 4).

Compressor monitoring further allows for improved conditional and/orconstrained ventilation (process 516 of FIG. 5 as described above, suchas ventilation permitted only when the system is heating or cooling asdescribed above with respect to FIG. 7) during the ventilation call 512of FIG. 5. For example, as shown in the example of FIG. 7, conditionalventilation for cooling as indicated by the “Y” signal is set to be ineffect at 85° F. or higher (indicated as temperature above 712 in FIG.7). In some exemplary implementations, for relative humidity (RH)conditions above a limit of 50%, compressor-on may be required forventilation to take place. Conditions above a RH of 55% may willrestrict ventilation (to, e.g., 25%) until the RH value drops below 50%.This function would allow ventilation only when the system is working toremove humidity (compressor is active). The 25% reduction in ventilationbased on elevated temperatures is also linked to the compressor signal.The same conditions can be said about the heating conditions. Howeverthe operation for ventilation is a bit different. When outsidetemperatures are below 40° F. (heating is required for ventilation inall three climate categories). This is also the temperature setpoint fordehumidification function. The original software had this set point at32° F. Depending on climate zone chosen, this function would not be veryeffective. The change in set point to activation the dehumidificationsetting will improve the effective potential of this function. Thealgorithm was also improved in the tracking of humidity control when thedehumidification is enabled. Dehumidification will not be active untilthe RH value rises above 55%. At any given point in time thatventilation is active, a rise in RH after the ventilation cycle hasstarted will terminate the ventilation function and hold off any furtheractivity that may be result of the rise in humidity.

Examples of conditional/restrained ventilation based on temperature forthese implementations utilizing the compressor signal are describedbelow. When the ODT sensor (126 of FIG. 1) detects temperature higherthan 85° F., the FAV controller may require compressor activity asmonitored by the Y signal for the ventilation call to be active. Whenthe ODT sensor detects temperature higher than 90° F., the FAVcontroller may require compressor activity as monitored by the Y signalfor the ventilation call to be active and at the same time reduce theventilation to a limited level (e.g., 25%). When the ODT sensor detectstemperature higher than 100° F., the FAV controller may prohibit theventilation regardless of the compressor signal. When the ODT sensordetects temperature lower than 40° F., the FAV controller may requireeither compressor activity as monitored by the Y signal or heatingactivity (as monitored via the W signal for the ventilation call to beactive. This configuration covers both a conventional cooling/heatingsystem and a heat pump system (where both heating signal and coolingsignal would be provided by compressor signal). When the ODT sensordetects temperature lower than a predetermined ventilation restrictingtemperature (e.g., 25° F.), the FAV controller may require eithercompressor activity or heating activity for ventilation to be active andat the same time reduce the ventilation to a limited level (e.g., 25%).When the ODT sensor detects temperature lower than, e.g., 0° F., the FAVcontroller may prohibit ventilation. For ODT temperature notrestricted/conditioned above, ventilation call may be remain activatedwithout restriction and regardless of the compressor signal.

Examples of conditional/restrained ventilation based on relativehumidity for these implementations utilizing the compressor signal forODT temperature above 70° F. are further described below. When theindoor RH is below, e.g., 50%, the FAV controller may not furtherrestrict ventilation beyond what was described above for temperaturerestriction. When the indoor RH is above 50% but below, e.g., 55%, theFAV may require compressor to be active for ventilation via the Vterminal (234 of FIG. 2, for controlling the damper 124 of FIG. 1) butdoes not require the compressor to be active for ventilation via the Eterminal (232 of FIG. 2 for controlling the energy efficient exhaustappliance). When the indoor RH is above 55% but below, e.g., 60%, TheFAV controller may require compressor activity for ventilation via bothV and E terminals and may further reduce ventilation to, e.g., 25%. Whenthe indoor RH is above 60%, the FAV controller may prohibit ventilation.In one implementation, this prohibition may lock in the RH limit suchthat it cannot be released until indoor RH falls below 50% for theventilation to be reactivated.

Examples of conditional/restrained ventilation based on relativehumidity for these implementations utilizing the compressor signal forODT temperature below 70° F. are further described below. When theindoor RH is below, e.g., 50%, the FAV controller may not furtherrestrict ventilation. When the indoor RH is above 50% but below, e.g.,55%, a dehumidification function may be enabled but not active unlessoutdoor temperature is below 40° F. When the indoor RH is above 55%, adehumidification function may be activated and ventilation may bepermitted if heat (W) or compressor (Y) signals are present. Thedehumidification process requires that indoor RH drops during a timedduration while ventilation is active. If humidity levels rise, whiledehumidification process is active, ventilation will be disabled untilindoor RH falls below 50%. When outdoor temperature rises above 40° F.,the dehumidification mode may be disabled and ventilation may not bepermitted.

An exemplary logic flow for ventilation call conditioned on compressorsignal Y for ODT higher than 70° F. as described above is shown as 800in FIG. 8. In particular, ventilation call of 512 in FIG. 5 starts at802. The FAV controller first determine whether the compressor activityis required for the ventilation to be activated (with exemplaryscenarios requiring compressor activity discussed above) at 804. If thecompressor activity is not required for ventilation, the FAV controllerfurther checks other ventilation constraints (808). If there are otherconstraints that prevent ventilation from being activated, the FVAcontroller keep monitoring system changes (810). If FAV controllerdetermines that the compressor activity is required in 804, it thenfurther determine whether the compressor is active by monitoring Ysignal (806). If the FAV controller determines that compressor is notactive, it the continue to monitor compressor signal to indicatecompressor activity (812). If the FAV controller determines thatcompressor activity is required (804) and the Y signal is active (808),or determines that the compressor activity is not required (804) and noother ventilation restraints are present (808), it proceed in 814 toactivate the ventilation by calculating the ventilation run time duringthe current ventilation call and activate the V (ventilation damper) andE (energy efficient exhaust appliance) based on energy mode as set ofthe dipswitches 250 in FIG. 2. The FAV may further monitor in 814 the RHand deactivate the V and E terminals under certain RH condition, forexample, if RH rise above, e.g., 60%.

An exemplary logic flow for ventilation call conditioned on thecompressor (Y) and heating (W) signal for ODT lower than 70° F. is shownin FIG. 9. The logic flow of FIG. 9 is similar to the logic flow shownin FIG. 8, except that in 904, whether heading rather than cooling isrequired during the ventilation call, and in 914, the RH and ODTconditions for deactivating the ventilation would be different from theRH conditions for deactivation of the ventilation in 814 of FIG. 8.

The FAV controller disclosed above is configured to independentlymonitor up to four exhaust appliances. The FAV controller may monitor awide range of types of appliances, with their operational flow rateflexibly configured via the FRSDs. Each of the four pairs of monitoringterminals may be wired to monitor a group of appliances rather than asingle appliance. As such, the FAV controller disclosed above may becapable of monitoring more than four individual appliances, as long asthe sum of the flow rates within each appliance group does not exceedthe maximum setting of the corresponding FRSD. The FAV controllerfurther provides control over a single or a group of exhaust appliancesand control over the central fan, bypassing the thermostat if needed forventilation. The ventilation is controlled periodically to satisfy atarget continuation FAV flow rate subject to constraints and conditionsdesigned to protect the furnace plenum from condensation. Theconstraints and conditions are monitored by the FAV controller viavarious humidity and temperature sensors. The monitored operation ofvarious exhaust appliances is credited to the ventilation target,providing energy savings and preventing over ventilation. The FAVcontroller further provides a dual mode ventilation control (normal modeand energy saving mode) and multiple climate modes.

In some other implementations, a progressive restraint on ventilationdruing ventilation calls may be used depending on the RH level. Forexample, the progressive ventilation may be implemented in a pluralityof progressive levels (rather an a two-level implementation of either25% or 100% discussed in the implementations above). In particular, whenthe FAV controller determines to proceed with a ventilation call duringa ventilation cycle, it may calculate the ventilation run time and thenreduce the run time according to the RH level as monitored by the FAV.For example, when the RH is below 50%, the ventilation run time may notbe reduced. When the RH is between e.g., 50% and 52%, the ventilationrun time during the current ventilation cycle may be reduced to 75%.When the RH is between e.g., 52% and 55%, the ventilation run timeduring the current ventilation cycle may be reduced to 50%. When the RHis between e.g., 55% and 60%, the ventilation run time during thecurrent ventilation cycle may be reduced to 25%. When the RH is abovee.g., 60%, the ventilation may be prohibited during the currentventilation cycle. The progressive ranges of RH and corresponding amountof ventilation reduction above are mere examples and are not limiting.Progressive ventilation with finer granularity or continuous progressionmay be similarly implemented. The progressive ventilation may beimplemented in the cooling mode or both in the cooling mode and heatingmode. Such progressive ventilation may be particularly relevant to thecooling mode because throttling the amount of ventilation progressivelydownward depending on RH levels would provide less damaging condensationat the furnace plenum during cooling where the furnace is not active.

In yet some other implementations and when a ventilation prohibitioncondition occurs (e.g., when RH is above 60%, or under any otherprohibition condition discussed or not discussed above), the ventilationwould be prohibited but the FAV controller may allow forced ventilationwhen the prohibition period persists longer than a preset threshold. Forexample, if the prohibition condition persists for more than, e.g., 4hours, the FAV may allow one or more cycles of ventilation. For example,the FAV may reset a timer and begin countdown when a prohibition starts.If the prohibition condition persists and no ventilation is performedduring the countdown, the FAV may allow ventilation after the timercounts down to zero. Such forced ventilation may be permitted for one ormore ventilation cycles and if the prohibition condition persists, theFAV may restore prohibition, reset the timer, and begin a nextcountdown. Such ventilation under prohibition condition is aimed atproviding at least some amount of ventilation during an otherwise longprohibition stretch. In some implementations, such ventilation may beprovided at a reduced level, e.g., 25%. In order to reduce potentiallife-reducing damage to the heating/cooling system, in someimplementations, such ventilation may only be allowed when cooling orheating is active as monitored by the FAV controller as discussed above.

In the detailed disclosure above, terminology may be understood at leastin part from usage in context. For example, terms, such as “and”, “or”,or “and/or,” as used herein may include a variety of meanings that maydepend at least in part upon the context in which such terms are used.Typically, “or” if used to associate a list, such as A, B or C, isintended to mean A, B, and C, here used in the inclusive sense, as wellas A, B or C, here used in the exclusive sense. In addition, the term“one or more” as used herein, depending at least in part upon context,may be used to describe any feature, structure, or characteristic in asingular sense or may be used to describe combinations of features,structures or characteristics in a plural sense. Similarly, terms, suchas “a,” “an,” or “the,” again, may be understood to convey a singularusage or to convey a plural usage, depending at least in part uponcontext. In addition, the term “based on” may be understood as notnecessarily intended to convey an exclusive set of factors and may,instead, allow for existence of additional factors not necessarilyexpressly described, again, depending at least in part on context.

The illustrations of the implementations described herein are intendedto provide a general understanding of the structure of the variousembodiments. The illustrations are not intended to serve as a completedescription of all of the elements and features of apparatus and systemsthat utilize the structures or methods described herein. Many otherimplementations may be apparent to those of skill in the art uponreviewing the disclosure. Other implementations may be utilized andderived from the disclosure, such that structural and logicalsubstitutions and changes may be made without departing from the scopeof the disclosure. Additionally, the illustrations are merelyrepresentational and may not be drawn to scale. Certain proportionswithin the illustrations may be exaggerated, while other proportions maybe minimized. Accordingly, the disclosure and the figures are to beregarded as illustrative rather than restrictive.

What is claimed is:
 1. A fresh air ventilation control (FAVC) systemcomprising: a first input device for setting a first fresh airventilation flow rate (FAVFR) as a target for a continuous fresh airventilation; a second input device for setting a second FAVFR of an airhandler when in operation; a third input device for setting a thirdFAVFR of a first ventilation appliance when in operation; a firstelectric interface adapted to couple to the air handler and a thermostatfor controlling the air handler; a second electric interface adapted tocouple to a sensor for monitoring an operation of the first ventilationappliance; a system circuitry configured to, in a consecutive firstcycle and second cycle of multiple control cycles: monitor an effectiveFAVFR of the first ventilation appliance during the first cycle basedthe third FAVFR and an operation time of the first ventilation applianceduring the first cycle measured via the second electric interface;monitor, via the first electric interface, an effective FAVFR of the airhandler during the second cycle based on the second FAVFR and anoperation time of the air handler during the second cycle under thecontrol of the thermostat; and generate a control signal for obtainingsupplemental fresh air ventilation during the second cycle when a sum ofthe effective FAVFR of the ventilation appliance and the effective FAVFRof the air handler is less than the first FAVFR.
 2. The FAVC system ofclaim 1, further comprising: a fourth input device for setting a fourthFAVFR of a second ventilation appliance when in operation; a thirdelectric interface adapted to couple to the second ventilationappliance; and a mode selector for setting the FAVC system to one of anormal mode and an energy-saving mode, wherein the control signal issent to the second ventilation appliance via the third electricinterface for obtaining the supplemental fresh air ventilation and isprevented from being sent to the air handler when the mode selector isset to the energy-saving mode, and is sent to both the secondventilation appliance and the air handler for obtaining the supplementalfresh air ventilation when the mode selector is set to the normal mode.3. The FAVC system of claim 2, wherein a duration of the control signalis determined by: a difference between the first FAVFR and the sum ofthe effective FAVFR of the ventilation appliance and the effective FAVFRof the air handler; and the fourth FAVFR when the mode selector is setto the energy-saving mode or a sum of the second FAVFR and the fourthFAVFR when the mode selector is set to the normal mode.
 4. The FAVCsystem of claim 1, further comprising a fourth electric interfaceadapted to couple to a motorized damper disposed in a fresh airventilation path coupled to a return path of the air handler, whereinthe system circuitry is further configured to keep the motorized damperopen during the supplemental fresh air ventilation.
 5. The FAVC systemof claim 4, further comprising: a third electric interface adapted tocouple to a second ventilation appliance, wherein the system circuitryis further configured to monitor the second ventilation appliance viathe third electric interface and keep the motorized damper open when thesecond ventilation appliance is in operation.
 6. The FAVC system ofclaim 1, further comprising a fourth electric interface adapted tocouple to a thermometer for monitoring temperature of fresh air in aventilation path coupled to a return path of the air handler, wherein aduration of the control signal for obtaining supplemental fresh airventilation is dependent on the monitored temperature.
 7. The FAVCsystem of claim 6, wherein the duration of the control signal is reducedto zero when the monitored temperature is lower than a firstpredetermined temperature threshold or higher than a secondpredetermined temperature threshold.
 8. The FAVC system of claim 1,further comprising: a fourth electric interface adapted to couple to athermometer for monitoring temperature of fresh air in a ventilationpath coupled to a return path of the air handler; and a humidity sensorfor monitoring relatively humidity of a return air of the air handler,wherein a duration of the control signal for obtaining supplementalfresh air ventilation is dependent on the monitored temperature andrelative humidity.
 9. The FAVC system of claim 8, wherein the durationof the control signal is reduced by a predetermined proportion for apredetermined set of ranges for the monitored temperature and relativehumidity.
 10. The FAVC system of claim 1: wherein the thermostatcontrols the air handler to operate in one of a cooling and a heatingmode; wherein the second input device comprises a first input componentand a second input component for independently setting a cooling FAVFRof the air handler when operating in the cooling mode and a heatingFAVFR of the air handler when operating in the heating mode; wherein thesystem circuitry is further configured to monitor an operating mode ofthe air handler via the first electric interface; and wherein the secondFAVFR comprises one of the cooling FAVFR and the heating FAVFR incorrespondence with the monitored operating mode of the air handler. 11.A fresh air ventilation control (FAVC) system, comprising: a first inputdevice for setting a first fresh air ventilation flow rate (FAVFR) as atarget for a continuous fresh air ventilation; a second input device forsetting a second FAVFR of an air handler when in operation; a thirdinput device for setting a third FAVFR of a first ventilation appliancewhen in operation; a fourth input device for setting a fourth FAVFR of asecond ventilation appliance when in operation; a first electricinterface adapted to couple to the air handler and a thermostat forcontrolling the air handler; a second electric interface adapted tocouple to a sensor for monitoring an operation of the first ventilationappliance; a third electric interface adapted to couple to the secondventilation appliance; a fourth electric interface adapted to couple toa thermometer for monitoring temperature of fresh air in a fresh airventilation path coupled to a return path of the air handler; a fifthelectric interface adapted to couple to a motorized damper disposed inthe fresh air ventilation path; and a system circuitry configured to:monitor operation times of the air handler, the first ventilationappliance, the second ventilation appliance, and a measurement of thethermometer via the first, the second, the third, and the fourthelectric interfaces; and control the motorized damper, and/or the airhandler, and/or the second ventilation appliance via the first, thethird, and the fifth electric interfaces.
 12. The FAVC system of claim11, wherein the system circuitry is further configured to keep themotorized damper open and keep a central fan of the air handler on whenthe second ventilation appliance is in operation.
 13. The FAVC system ofclaim 11, wherein the system circuity, when configured to control theair handler and the motorized damper and/or the second ventilationappliance, is configured to control air handler and the motorized damperand/or the second ventilation appliance in periodic ventilation cycles.14. The FAVC system of claim 13, wherein the system circuitry isconfigured to control the air handler and the motorized damper and/orthe second ventilation appliance to meet a predetermined ventilationtarget in a ventilation cycle.
 15. The FAVC system of claim 14, whereinthe system circuitry is configured to credit the monitored operationtime of the first ventilation appliance in a first ventilation cycle tothe predetermined ventilation target of a second ventilation cyclefollowing the first ventilation cycle.
 16. The FAVC system of claim 11,further comprising a mode selector for setting the FAVC system intoeither a normal control mode or an energy saving control mode.
 17. TheFAVC system of claim 16, wherein, when the FAVC system is set in theenergy saving mode, the FAVC system is configured to control themotorized damper and/or the second ventilation appliance and isconfigured to leave a control of the air handler to the thermostatunless the air handler is idle for a predetermined idle time.
 18. TheFAVC system of claim 16, wherein, when the FAVC system is set in thenormal mode, the FAVC system is configured to control the motorizeddamper and the second ventilation appliance, and is further configuredto control the air handler in conjunction with the thermostat.
 19. TheFAVC system of claim 11, further comprising a humidity sensor formonitoring a relative humidity of air in the return path of the airhandler, wherein a set of constraints based on the monitored relativehumidity and the measurement of the thermometer is applied when the FAVCsystem is configured to control the motorized damper, and/or the airhandler, and/or the second ventilation appliance.
 20. The FAVC system ofclaim 11, wherein the system circuitry is further configured to disablecontrol over the motorized damper, the air handler, and the secondventilation appliance when the measurement of the thermometer is above apredefined high temperature threshold or below a predefined lowtemperature threshold.